Unleaded, regular or "super", the diference?

This is not e30 particular, but technical nevertheless.
I've been advised by the mechanic to always use unleaded98 on my car, which is a bit more expensive than the regular unleaded95.
On my carburated car, does it makes a real difference? Any major disadvantages?

QuoteJose Pinto
This is not e30 particular, but technical nevertheless.
I've been advised by the mechanic to always use unleaded98 on my car, which is a bit more expensive than the regular unleaded95.
On my carburated car, does it makes a real difference? Any major disadvantages?

In my 2002's I always got better mileage with the better grade fuel, seemed to run better too. I've always also though that gas was such poor quality using the better grade was a good idea, cleaner.

This is a tricky subject though, I bet lots of people are going to say there is no difference, it'll be interesting to see.

The octane (i.e. RON) rating is a measure of how resistant a fuel is to pre-igniting, i.e. knocking. The higher the octane rating, the more resistant the fuel is to knocking. Cars that require higher octane fuel generally have high compression ratios, advanced timing, or both. For example, lots of people put aftermarket chips in their BMWs for more power. These chips work by partly advancing the timing, necessitating the use of higher octane fuel. For another example, lots of performance cars (especially those of a generation ago) produce more power by running high compression ratios, so they also require high octane fuel to avoid knocking.

The simplest way to tell whether you need higher octane fuel is to try low octane fuel and see if the engine starts knocking. If so, use a higher octane. Since modern cars usually have knock sensors and retard the timing if they sense knocking, you'll instead experience a loss of power as the ECU does its job and prevents knocking.

Because of this, and because many performance cars with high-compression engines require high octane fuel, lots of people are under the mistaken belief that the higher the octane, the more energy the fuel has and the more power you get. This is not true -- the ONLY thing higher octane does is reduce knocking (because it ignites less easily).

If your car has a carburetor, I'm guessing it's old enough that it doesn't have a knock sensor. If that's the case, if you're not getting any knocking with regular, then I wouldn't bother with the higher octane stuff. There's no harm in using the premium stuff, other than the harm to your wallet. If it does knock, then I would switch.

Personally I run regular (87 octane) gas in all my cars, including the E30, but when I run my Miata on the track, I give it 93 octane (the North American ratings are lower than the rest of the world RON ratings), because it's running at 5000-7000 RPM for hours each day. It doesn't give it any more power, but I like the extra insurance. Knocking in that case could be extremely harmful to the engine!

I am surprised that the mechanic told you to run unleaded, I have always run my e30 on super, or leaded petrol, after all, when these motors were designed and built, unleaded didn't exist yet, unless you guys in Europe don't get leaded fuel any more, in which case +1 on what Dave said.
I ran my e30 on unleaded once, and I can tell you, I am sure it did not like it, it did all sorts of strange things, or maybe it was placebo effect and it was all in my head, but I don't think so, I know my car.
I will never put unleaded in her again.
And the M40 motor has a very low compression ratio, 8.8:1, I am sure it would run on cooking oil.

Gasoline is has different formulations in different parts of the world. In Canada and the US, the government mandates what goes into the fuels so there is little difference from one brand to the next. There is a noticeable difference in the Canadian fuel vs the US fuel; something to do with sulphur content or so I was lead to believe.

There are also differences in the E30 motors depending on the region they are built in or for.

All North American E30s, including the M, should run just fine on regular fuel(at what ever the Octane rating or RON). If the cars are pinging, then it is most likely because of carbon build up or some component being out of spec.
My iX only exhibited 'knock' once and I took care of it with Techron in the gas and a really hard drive that blew the carbon cobwebs out the exhaust
Never had a problem after that.

QuoteDave_G
The octane (i.e. RON) rating is a measure of how resistant a fuel is to pre-igniting, i.e. knocking. The higher the octane rating, the more resistant the fuel is to knocking. Cars that require higher octane fuel generally have high compression ratios, advanced timing, or both. For example, lots of people put aftermarket chips in their BMWs for more power. These chips work by partly advancing the timing, necessitating the use of higher octane fuel. For another example, lots of performance cars (especially those of a generation ago) produce more power by running high compression ratios, so they also require high octane fuel to avoid knocking.

The simplest way to tell whether you need higher octane fuel is to try low octane fuel and see if the engine starts knocking. If so, use a higher octane. Since modern cars usually have knock sensors and retard the timing if they sense knocking, you'll instead experience a loss of power as the ECU does its job and prevents knocking.

Because of this, and because many performance cars with high-compression engines require high octane fuel, lots of people are under the mistaken belief that the higher the octane, the more energy the fuel has and the more power you get. This is not true -- the ONLY thing higher octane does is reduce knocking (because it ignites less easily).

If your car has a carburetor, I'm guessing it's old enough that it doesn't have a knock sensor. If that's the case, if you're not getting any knocking with regular, then I wouldn't bother with the higher octane stuff. There's no harm in using the premium stuff, other than the harm to your wallet. If it does knock, then I would switch.

Personally I run regular (87 octane) gas in all my cars, including the E30, but when I run my Miata on the track, I give it 93 octane (the North American ratings are lower than the rest of the world RON ratings), because it's running at 5000-7000 RPM for hours each day. It doesn't give it any more power, but I like the extra insurance. Knocking in that case could be extremely harmful to the engine!

My car has no sensors, it uses a membrane measuring the vacuum on the engine to advance the ignition, next to the distributor cap and rotor.
I used sometimes regular, but to test things right i would need to run several tanks of regular and keep track of consumption to try to notice any increase, ant then compare that against the difference in price/litter.

QuoteFlyboy
I am surprised that the mechanic told you to run unleaded, I have always run my e30 on super, or leaded petrol, after all, when these motors were designed and built, unleaded didn't exist yet, unless you guys in Europe don't get leaded fuel any more, in which case +1 on what Dave said.
I ran my e30 on unleaded once, and I can tell you, I am sure it did not like it, it did all sorts of strange things, or maybe it was placebo effect and it was all in my head, but I don't think so, I know my car. I will never put unleaded in her again.

Unless SA engines are purposedly built locally, most BMW can use unleaded, check with the dealer, they have lists of cars that really need leaded.

QuoteFlyboyAnd the M40 motor has a very low compression ratio, 8.8:1, I am sure it would run on cooking oil.

I wouldn't try that! If it was a Diesel, it could. In case it had high compression, there would be advantage in converting to alcohol, like they do in Brazil.

QuoteArcheo-peteriX
Gasoline is has different formulations in different parts of the world. In Canada and the US, the government mandates what goes into the fuels so there is little difference from one brand to the next. There is a noticeable difference in the Canadian fuel vs the US fuel; something to do with sulphur content or so I was lead to believe.

There are also differences in the E30 motors depending on the region they are built in or for.

All North American E30s, including the M, should run just fine on regular fuel(at what ever the Octane rating or RON). If the cars are pinging, then it is most likely because of carbon build up or some component being out of spec.
My iX only exhibited 'knock' once and I took care of it with Techron in the gas and a really hard drive that blew the carbon cobwebs out the exhaust
Never had a problem after that.

Sometimes i go to Spain anf fill up there (80km drive, it's a bit cheaper there). I feel no change in car behavior or average consumption.

QuoteJose Pinto
Sometimes i go to Spain anf fill up there (80km drive, it's a bit cheaper there). I feel no change in car behavior or average consumption.

Likewise, when I'm in Canada and fill up there, I've never noticed any difference in the car. This includes running on the track, and I would expect if anything was going to show up, it would show up there.

I'm not positive about the sulphur regulations in gasoline, but I think the difference is not between the U.S. and Canada, but varies among the different states and provinces. Regardless, I don't think sulphur does anything other than pollute the air -- I could be wrong, but I don't think it affects an engine's performance.

I remember when the first V8s came to the US and the engines built with NaSil cylinders were wearing out very prematurely. It was reported by BMW that it was because of the high sulphur content of US gasoline compared to that used in Germany and I assume other parts of Europe.

Many Canadian car dealers will not honour warranties if they find out that the car has been regularly using US fuel. There was a particular incident here about 10 years ago with a Honda that developed catastrophic engine failure. When the dealer found out from the customer that she regularly filled up across the border(a 5 minute drive); they disclaimed the warranty. The owner took the dealer and Honda Canada to court but lost. I don't remember the details but do remember the case.

QuoteFlyboy
I am surprised that the mechanic told you to run unleaded, I have always run my e30 on super, or leaded petrol, after all, when these motors were designed and built, unleaded didn't exist yet, unless you guys in Europe don't get leaded fuel any more, in which case +1 on what Dave said.
I ran my e30 on unleaded once, and I can tell you, I am sure it did not like it, it did all sorts of strange things, or maybe it was placebo effect and it was all in my head, but I don't think so, I know my car.
I will never put unleaded in her again.
And the M40 motor has a very low compression ratio, 8.8:1, I am sure it would run on cooking oil.

Hey Stan, I think the E30 cars were intended to run unleaded fuel. The gas tank fill has that smaller fill tube so the leaded pump nozzle would not work. My 1983 323 had the same set-up.... Here in the states anyway.

Quoterkj
Hey Stan, I think the E30 cars were intended to run unleaded fuel. The gas tank fill has that smaller fill tube so the leaded pump nozzle would not work. My 1983 323 had the same set-up.... Here in the states anyway.

Yeah, this all got me wondering when leaded gasoline was phased out in the U.S. The phase-out began 1976, and was complete by 1986. So during the early years of the E30, leaded gas was available, but rare by that point, so it was clearly in BMW's best interest to design the cars for unleaded.

I don't think there aren't many places left in the world where leaded gas is still legal on the roads. BTW, lead acts as an anti-knock compound, which raises the octane. At race tracks in the U.S. you can still get leaded 110 octane race fuel (at about three times the price of street-legal gas).

Quoterkj
Hey Stan, I think the E30 cars were intended to run unleaded fuel. The gas tank fill has that smaller fill tube so the leaded pump nozzle would not work. My 1983 323 had the same set-up.... Here in the states anyway.

Yeah, this all got me wondering when leaded gasoline was phased out in the U.S. The phase-out began 1976, and was complete by 1986. So during the early years of the E30, leaded gas was available, but rare by that point, so it was clearly in BMW's best interest to design the cars for unleaded.

I don't think there aren't many places left in the world where leaded gas is still legal on the roads. BTW, lead acts as an anti-knock compound, which raises the octane. At race tracks in the U.S. you can still get leaded 110 octane race fuel (at about three times the price of street-legal gas).

Okay, I have to respectfully disagree with some of what you say Dave; in new york the Bmw's started coming through recommending , no, specifying, unleaded fuels in 1983. It said so right on the inside of the gas lid door on the E30.

I was doing grey market Porsche' from 82-85 and one of the stickers we had to install, if they didn't already have them, was the unleaded fuel on the fuel lid door and they all had the smaller fuel pipe.

I think even the 320 Bmw started with the unleaded fuel, I believe they carried the small fill tube also.

Quoterkj
Okay, I have to respectfully disagree with some of what you say Dave; in new york the Bmw's started coming through recommending , no, specifying, unleaded fuels in 1983. It said so right on the inside of the gas lid door on the E30.

You can disagree if you like, but that's actually what I was trying to say, so I think we're actually in agreement.

Quoterkj
Okay, I have to respectfully disagree with some of what you say Dave; in new york the Bmw's started coming through recommending , no, specifying, unleaded fuels in 1983. It said so right on the inside of the gas lid door on the E30.

You can disagree if you like, but that's actually what I was trying to say, so I think we're actually in agreement.

I guess it is very market specific, none of the E30's here have small filler necks or anything like that, you could put whatever pipe you liked in.
Although we have unleaded 93,95 and 98, and most cars use the stuff, leaded is still freely available at all our filling stations, and cheaper than unleaded, to boot.
When they introduced unleaded, the discounted it to try and sweeten the deal to get people to swing over, but that changed a long time ago and unleaded is now, on average 30c more expensive a litre than leaded.
Of course not only is the lead a knock inhibitor, more importantly it is a lubricant, I remember when they changed the Avgas for the the aircraft from 100 leaded to 100LL (Low Lead), the aircraft were dropping valves left right and center, until they sorted out the recipe.
So as long as leaded fuel is available, that is what I will be using, I think unleaded is vile stuff anyway, and the cocktail of chemicals in it to replace the lead, is far more harmful to the environment than the lead ever was.
But, yes, I would imagine, the little 318, with its low compression and its knock sensor, along with the timing controlled by the ECU could run on unleaded without a problem, seeing that most the good folk here drive 325's and the like, with higher performance motors without a problem.
I am just glad we still have choices here, and don't have folk like the EPA and the Govt. telling us what is and isn't good for me, and legislating what I can and can't use.

QuoteFlyboy
I am just glad we still have choices here, and don't have folk like the EPA and the Govt. telling us what is and isn't good for me, and legislating what I can and can't use.

Lead was banned from gasoline for environmental reasons. Apparently it's really not good to be spewing lead out of a bazillion tailpipes.

Valve seats and guides had to be re-designed to cope with the absence of lead as lubricant, and fuels had to be reformulated to find substitute octane enhancers, many of which are just as lethal as lead.

Filler neck restrictions, and matching smaller filler nozzles, were mandated in order to prevent inadvertent filling with leaded fuel from pumps with the old larger sized nozzles. Later we also mandated anti-syphoning features in the filler neck to prevent thieves from accidentally poisonin themselves with Ethanol-enhanced fuels.

Leaded fuels were eventually banned altogether.

Our cars would probably still run fine on leaded fuel, if you can get it past the filler neck restriction. However, the lead is doubly bad for the environment. Not only does the spent lead pollute the environment, but it also poisons the catalyst in catalytic converters thereby allowing other preventable hydrocarbon and nitrous oxide exhaust pollutants into the environment.